Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Milwaukee/Sullivan WI
303 PM CDT Tuesday Jul 7 2015
Tonight and Wednesday...forecast confidence...high
Hazy skies in between afternoon cumulus indicate smoke aloft is
still hanging around. Fortunately...daytime mixing has removed most
of the smoke near the surface. Hoping enough of the smoke has moved
on that it will not have an impact near the surface tonight.
High pressure will move overhead tonight...with subsidence from the
high and loss of daytime heating allowing skies to become mostly
clear. Could see a little fog in low lying spots later tonight into
early Wednesday morning...with highest confidence in any patchy fog within
the Wisconsin River Valley. The light winds and mostly clear skies
will combine with a drier/cooler airmass for well below normal low
Skies will be mostly sunny into the afternoon Wednesday...with some
high level clouds increasing across at least the south during the
afternoon as low pressure moves into the region. With 925 mb temperatures
only in the 14-16c range tomorrow afternoon...high temperatures are
expected to be several degrees below normal once again.
Wednesday night through Thursday...forecast confidence medium.
Models are indicating a modest 500 mb shortwave trough to move
northeast through MO and into central Illinois Wednesday evening. There
is some uncertainty regarding how far north the moisture from
associated surface low pressure will reach as the 12z GFS keeps quantitative precipitation forecast
south of S WI while the 15z sref and 12z ecwmf brings a small
surge of precipitation into our southeast counties. Frontogenetical forcing
strength ranges a bit across the models. Contemplated removing
probability of precipitation altogether across the southeast...but with the sref and European model (ecmwf)
progging some chances for some precipitation...kept slight chances of
precipitation in for now.
Once shortwave moves off to the east...more zonal middle-level flow and
surface high pressure will keep conditions quiet and dry during the day
Thursday night through Saturday...forecast confidence medium
Dry conditions look to persist Thursday night and Friday morning
until surface warm front and 500 mb shortwave trough develops over
the OK Panhandle region and translates northeast into Iowa Friday
morning. Strong 850 mb warm air advection looks to accompany the
shortwave. Models are a little uncertain on the precise location
of the 500 mb shortwave...with the GFS bringing it over north WI...NAM
over S WI...and the European model (ecmwf) and Canadian models taking it over north Illinois.
The best forcing will arrive later in the day Friday as enhanced
frontogenetical forcing moves in along the baroclinic zone
associated with the surface warm front.
NAM and GFS seem to be in agreement on the timing of the
precipitation Friday afternoon and evening...while the European model (ecmwf)
delays precipitation until the morning hours Saturday. Chances of
precipitation should linger through the day Saturday as a weak
corridor of 850-700 mb q-vector convergence lingers. Went with the
NAM and GFS solutions for the probability of precipitation.
Long term...Saturday night through Tuesday...forecast confidence
The surface low pressure will move off to the east as a 500 mb
shortwave ridge develops to the west Saturday...helping to enhance
low level warm air advection. Some discrepancies do exist between the GFS and
European model (ecmwf) 925 mb temperatures as the GFS shows temperatures near 26c as a
result of the shortwave ridging. European model (ecmwf) 925 mb temperatures are not quite
as high...only 18c. This discrepancy makes it a little arduous to
pin down high temperatures for the weekend. The blended models are
showing highs for the weekend in the 80s...with middle 80s on Sunday.
Middle-level flow will slowly veer from the northwest as the 500 mb
shortwave ridge axis moves through the region Sunday. A series of
shortwave troughs are prognosticated to descend into Wisconsin as the
middle-level winds veer. These shortwaves look to keep chances of
precipitation in the area through Sunday and Monday as the GFS and
European model (ecmwf) are developing quantitative precipitation forecast along the axis of the 500 mb flow and
shortwaves. This 500 mb flow begins to moderate slightly during
the day Tuesday according to the GFS.
Aviation/00z tafs/...high pressure will move overhead
tonight...bringing quiet conditions to southern Wisconsin through
the day Wednesday. The skies do remain a bit hazy this
afternoon...but hoping enough of the smoke has moved on that it
will not have an impact near the surface tonight. Could see some
patchy fog in low lying areas later tonight into early Wednesday
morning...particularly within the Wisconsin River Valley.
Winds will ease later this afternoon into the evening...allowing
waves to subside. A Small Craft Advisory remains from Port
Washington southward until 00z early this evening...and this
expiration time still seems reasonable.
Winds and waves will be of little concern Wednesday under high
A beach hazard statement continues through 00z early this evening
for the beaches of Ozaukee...Milwaukee...Racine...and Kenosha
counties due to 3 to 5 foot waves producing dangerous currents along
the shore and especially near piers and breakwaters. Beach winds
will continue between 10 and 20 miles per hour from the north to
Winds will ease and waves subside this evening and overnight as high
pressure moves overhead.
WI...beach hazards statement until 7 PM CDT this evening for wiz060-
Lm...Small Craft Advisory until 7 PM CDT this evening for lmz644>646.
Tonight/Wednesday and aviation/marine...ddv
Wednesday night through Tuesday...jts